Hong W, Claire D, Yu Z, Yin S, Yu L and Yi Z
Soil quality has significant importance for the growth and sustainability of plants. However, due to the variability and diversity of soil characteristics, many trees suffered death according to their confrontation degree. Over the past several decades, Robinia pseudoacacia forests in the Yellow River delta of China, lose health and died without an obvious cause. This study focuses on evaluating the role of soil characteristics (moisture content, soil salinity content, soil bulk density, soil texture (the percentages of soil sand, soil silt, and soil clay) and pH value on the deterioration of health level of Robinia pseudoacacia forests in the area. To do so, three health levels such as healthy, medium dieback, and severe dieback forest were firstly classified based on the United States Department of Agriculture Forestry Bureau of crown condition classification guide and in situ survey, then soil properties in vertical direction were analyzed by five sampling points for each forest type from surface to the depth of 260 cm with eight layers (0-20 cm, 20-40 cm, 40-60 cm, 60-100 cm, 100-140 cm, 140-180 cm, 180-220 cm and 220-260 cm) for healthy and moderate dieback and 0- 220 cm depth with seven layers for severe dieback because the water occurred after 220 cm depth. The results indicated that there are significant differences in soil moisture content and soil conductivity among three forest health conditions. For a vertical change of soil characteristics only soil particle sizes (sand, silt and clay) had a significant difference in three forest health conditions. For system roots, absorptive roots were observed down to 230 cm depth for healthy Robinia pseudoacacia forest but moderate and severe dieback Robinia pseudoacacia forests, roots are found in the surface layer.